High-speed digital data links are commonly used in communication networks and parallel computers. They typically consist of input/output (I/O) drivers (senders) at one end and I/O receivers at the other end, with copper or optical interconnections in between. The quality of the links are measured by the data eye size (the size of the valid data sampling window) on the receivers. There are typically a set of physical parameters, for example, the driver strength, pre-emphasis amplitude on the sender node, and termination resistor value, on the receiver node that can be optimized to achieve an optimal data eye size for a given link at a designed operating frequency. However, the data eye size parameter is a statistical average which is collected over a long period of time (relative to a data bit time on the link), and does not contain any transient properties of the link. For example, if a link error occurs, the eye size parameter does not ascertain if this is caused by a single bit error that could be the result of random link noise, or a burst of several bits that could indicate a more serious link problem.
Therefore, a need exists to capture a bad or invalid data packet for future analysis. A further need exists to capture a corresponding good or valid packet for future analysis in conjunction with the bad packet.